Knowledge, attitudes and behaviours related to dietary salt among adults in the state of Victoria, Australia 2015

The World Health Organization recommends a dietary salt intake of no more than 5 g/day for healthy adults [1]. However globally most people consume much higher amounts of salt, well beyond the recommended level [2]. Previous studies estimate the average dietary salt intake for Australian adults is between 8 and 9 g/day, almost twice the recommended daily intake [3‐5]. This is similar to other industrialised countries, including the USA and UK, where salt consumption is approximately 10 g/day in males and 8 g/day in females [6, 7]. Approximately 75% of salt consumed in Western societies comes from processed foods and meals prepared in the food service industry, a much smaller proportion (15%) comes from salt added at the table and during cooking [8].

Sodium is an essential nutrient and for the body to function an intake of 10–20 mmol/d of sodium (salt equivalent 0.6–1.2 g/d) is required [8]. Excess salt intake is associated with the age-related rise in blood pressure [9]. In 2011–12 a third (32%) of Australian adults had hypertension [10], which represents a significant cause of premature death and disability in Australia [11]. Meta-analysis of randomised controlled trials have shown that among people with hypertension a 4.4 g/d reduction in salt intake (from a usual intake level of 9.5 g/d) significantly lowers systolic blood pressure by 5.4 mmHg millimetres of mercury (mm Hg) and diastolic blood pressure by 2.8 mmHg [12]. Among normotensive people a 4.4 g/d reduction (from a usual intake of 8.9 g/d) significantly lowers systolic and diastolic blood pressure by 2.4 mmHg and 1.0 mmHg, respectively [12]. Importantly, small shifts in the distribution of population blood pressure could provide considerable cardiovascular health gains [13, 14] and a 6 g/d reduction in salt intake would reduce stroke by 24% and coronary heart disease by 18% [14]. In 2013, Australia joined the WHO Member States in a global commitment to reduce population salt intake by 30% by the year 2025 [15].

Population salt reduction programs are usually multi-faceted, combining programs to change consumer behaviour with actions to get the food industry to reduce salt in foods [16]. The Victorian Health Promotion Foundation (VicHealth) is an independent statutory organisation funded by the State Government of Victoria. In 2015, VicHealth launched the multisector partnership to reduce population salt intake in Victoria through a combination of social marketing, industry engagement and research [17, 18]. This study was conducted to provide a baseline assessment of factors which influence salt intake in the Victorian population, to inform the planning, design and implementation of proposed salt reduction initiatives in Victoria. Specifically, the primary aim was to determine knowledge, attitudes and behaviours (KABs) related to salt intake among a sample of Victorian adults aged 18–65 years. In addition, we assessed the differences in salt related KABs by socio-demographic characteristics (i.e. sex, age group and socioeconomic status).

A total of 2559 participants agreed to complete the online survey. The response rate for the shopping centre intercept survey and online consumer research panel was 19.4% and 13.7%, respectively. It was not possible to determine the response rate for participants recruited via Facebook. Participants who did not answer any of the survey questions (n = 46, 1.8%) or did not complete the survey to the end were excluded from the analysis (n = 115, 4.5%). The final analytical sample was 2398 (93.7%). Of these participants, 1621 (67.6%) completed the survey through the online consumer research panel, 404 (16.8%) completed the survey via Facebook and 373 (15.6%) completed the survey at the shopping centres.

Just over half (56%) of the sample were female and the majority (80%) were born in Australia (Table 1). The average age of both males and females was 43 years and there was a relatively even distribution of participants across age groups. Approximately half of participants were from a high socio-economic background and 40% were in the healthy weight range category. In comparison to the Victorian population, people from a higher socioeconomic background, females and elderly aged 55–65 years were overrepresented, while younger people aged between 18 and 24 years were underrepresented (Table 1). The demographic characteristics of participants differed by recruitment method and these are shown in Additional file 2: Table S1.

Just under a third of the sample (29.4%) reported they had previously been diagnosed or suffered from a chronic condition, with the most common being high blood pressure (21.4%). National estimates for high blood pressure, based on a measured blood pressure reading of SBP ≥140 mmHg and/or DBP ≥90 mmHg or reported use of hypertensive medications, among Australian adults is 31.6% [32]. Of those with high blood pressure (n = 514), 74.9% reported taking medication to control their blood pressure. Two thirds (69.0%) of participants reported that they were the primary person responsible for household grocery shopping, whilst 21.0% shared the responsibility.

Our findings demonstrate that while certain aspects of salt related knowledge are well understood among Victorian adults, a number of gaps exist which vary across socio-demographic characteristics that could be targeted in consumer awareness campaigns. Consistent with past studies [33] most participants were aware of the harmful effect of excess salt on health and the link with particular conditions such as raised blood pressure and coronary heart disease. Fewer were aware of the link with other health conditions, notably about a third did not identify stroke as a related risk. It appears that the message of high blood pressure and heart disease as a determinant of a high salt intake is reaching the public but there is scope to raise greater awareness for stroke risk, particularly given stroke is the third leading cause of death in Australia [34] and the evidence linking high salt intake to stroke is well established [35].

Majority of participants were aware that most Australians eat too much salt, yet very few believed their own individual salt intake would exceed dietary recommendations. The finding, whereby consumers underestimate their own intake is consistently reported across other population groups [28, 29, 36, 37]. Consumers may misjudge their own intake for at least two reasons. Firstly, knowledge of dietary salt recommendations was poor. Secondly, although participants were aware that most salt comes from processed foods, a more thorough understanding may be lacking of how widespread salt is across the food supply and that everyday food items, such as bread and cereal products, can provide substantial amounts of salt to the diet. . There is a clear need to raise awareness of the current high salt intakes seen across the community as well as what foods contribute salt to the diet. In particular, efforts should be focused in reaching those sub-groups of the population which generally displayed less knowledge of these factors (i.e. males, younger to middle age adults (i.e. 25–44 years) and those of lower socioeconomic background.

Overall only 41% of participants believed that their health would improve if they reduced the amount of salt in their diet. Similarly, less than half were concerned about the amount of salt in their diet. These findings are not surprising, given the majority did not view their own intake as being high. Previous studies have shown that adults who believe salt reduction is important or who are concerned with the amount of salt in their diet are more likely to be taking action to reduce dietary salt [29] or engaging in salt related behaviours such as checking the sodium information on food labels and purchasing foods labelled salt reduced [26, 37]. Hence, shifting Victorians’ attitudes related to concern for dietary salt may be an important precursor for salt related behaviour change. Particularly, in those sub-groups where concern for salt in the diet was the lowest (e.g. males, younger participants (e.g. 18–24 years) and those of lower socioeconomic background. Just under half of survey participants reported difficulty understanding the sodium content on food labels and less than one third of participants regularly use food labels to check the salt content of foods, suggesting the sodium information on food labels is inadequate. In Australia, nutrition labels are required to display the sodium content of food per serve and per 100 g within the nutrition information panel (NIP) and the salt content is not provided [38]. This requires consumers to perform a calculation to determine the salt content of foods. However, only 33% of participants knew there was a difference between salt and sodium indicating it would be challenging for consumers to interpret how the sodium content of a food product relates to their overall salt intake. In the United Kingdom (UK) some food manufacturers opt to voluntarily provide information on the salt content (g) of a food product on the food label [39]. A similar approach in Australia could help consumers find lower salt foods, particularly in view of consumer awareness campaigns that target ‘salt’ rather than ‘sodium’. The survey also found that only one quarter of participants could correctly identify there were no health differences between regular salt and gourmet salts, suggesting that accurate information to inform food choices is not reaching consumers. These findings identify key issues to address in a public awareness campaign to enable individuals to understand and use food labels correctly and better inform healthy choices.

In Australia, the amount spent on fast food and dining out represents the highest component of household expenditure on food [40]. Participants reported a limited availability of low-sodium meal options when dining out, indicating that the restaurant and food service industry remain an important inclusion for future salt awareness and reduction programs. There is some evidence to indicate that the average sodium content of fast foods available from leading Australian chains fell, slightly, during the period 2009–2012 [41]. However, of note the average sodium content per serving remained unchanged during this period and at high levels (605 mg/serving) [41]. l.

Consumers attributed collective responsibility for reducing the amount of salt consumed by the Australian population, between individuals (89%) and the food industry (including food manufacturers (81%), fast food chains (77%) and chefs (76%). This study suggests there is strong consumer support for greater legislative and policy action on salt reduction in Australia.

Legislation which limits the amount of salt permitted (i.e. salt content targets) in processed foods has been identified as the most cost-effective strategy in the primary prevention of cardiovascular disease and lead to immediate and significant improvements in population health outcomes [42, 43]. hile voluntary salt content targets are a cost-effective approach, the introduction of mandatory salt content targets on processed foods would provide greater health benefits, averting 18% of Disability Adjusted Life Years (DALY) which are attributable to excess salt consumption in Australia [43]. This is 20 times greater than the proportion of DALYs (0.88%) which would be averted through the use of voluntary salt content targets [43]. [43]. If regulatory salt content limits were implemented, in addition to antihypertensive therapy, this would lead to a significant reduction in lifetime health expenditure saving $4.2 billion in Australia [42]. It is acknowledged that the addition of some salt to manufactured foods is required for functional purposes, including the control of microbial growth, gluten formation in bread and starter culture activity in cheese [44]. However the large variation in salt content within these products [45‐47] indicates the feasibility to reduce salt. The Australian Federal Government previously established voluntary sodium targets for 9 food categories under the Food and Health Dialogue which operated 2009–2013 [48]. While there is renewed opportunity for a greater reduction in sodium content of foods with the establishment of the Healthy Food Partnership in 2015, there are no indications that legislative changes to mandate sodium content are being considered by the federal government. Progressive targets and robust monitoring are required to increase the effectiveness of voluntary approach to salt reduction in the current political environment. A further opportunity to incentivise reformulation among food manufacturers is the use of marketing restrictions which are dependent on nutrient profiling. For example the National Heart Foundation of New Zealand’s “Pick the Tick” food label programme encouraged food manufacturers to reduce the amount of salt in breakfast cereals, breads and margarines, resulting in the removal of 33 t of salt from the food supply during 1998–1999, as food manufacturers reduced the amount of sodium in breakfast cereals, breads and margarines to qualify for use of the “Pick the Tick” logo on food products [49].

The reported use of discretionary salt in this sample of Victorian adults is higher compared to national estimates. In the 2011–12 Australian Health Survey 30% of adults reported adding salt during cooking ‘very often’ and 14% reported adding salt at the table ‘very often’ [50]. Comparatively, in the present study 38% reported adding salt during cooking ‘always/often’ and 25% reported adding salt at the table ‘always/often’. These differences may in part be explained by different response options between surveys and the inclusion of a wider age range of participants in the AHS (e.g. 19 years +). Importantly, it has been shown in Victorian adults that salt intake was 0.7 g/d higher in those who reported adding salt at the table and when cooking, compared to those who reported never or rarely adding salt [51]. Together, these findings indicate the need for education messages targeting discretionary salt practices among Victorian adults. Furthermore, our finding that discretionary salt use behaviours differed by socio-demographic characteristics (i.e. males and younger participants more likely to use table and cooking salt), indicate that such messages should be tailored for specific sub-groups of the population. In the UK, self-reported table salt use, which is subject to the inherent limitation of social desirability bias, among adults significantly declined following the implementation of the 2004 Food Standards Agency salt reduction campaign [51]. This was a comprehensive campaign that targeted consumer awareness of high salt intakes and food sources of salt as well as encouraged the food industry to reformulate food products to contain less salt. Importantly, findings from the UK demonstrate the potential for public awareness campaigns to shift discretionary salt use behaviours within the population. With regards to lowering population salt intake it is acknowledged that a combination of strategies is required, which includes product reformulation of lower sodium foods combined with strategies e.g. marketing and consumer education, that seeks to improve overall diet quality.

A strength of the current study includes the large sample size combined with the use of three recruitment methods to capture participants of varying socio-demographic background. However a limitation of the study is that compared to the Victorian population the sample was slightly over-represented of females and older participants, hence limiting the generalizability of the findings to the general population. Furthermore, the low response rate (19% via consumer research panel and 14% via online shopping centre) may introduce non-response bias, as survey responders may be more interested in diet and health. In addition the questionnaire was not validated, however the questions were modelled on those used in previous surveys [22‐31] and pilot testing was conducted to improve readability and participant comprehension. Finally, the survey was based on self-reported data, which may be different from actual behaviour.

This study provides a preliminary assessment of the relevant knowledge, attitudes and behaviours related to salt consumption among adults in the state of Victoria, Australia. Public concern about salt is low as many people remain unaware of their own salt intake. There are difficulties interpreting the sodium content of foods and identifying low salt meal options when dining out. A greater individual awareness of the excessive amount of salt consumed and increased availability of lower salt foods is likely to assist in reducing population salt intake. The study highlights the need to provide easy to understand information on the salt content of foods and lower salt levels in processed foods and food sold outside the home to enable consumers to reduce salt intake. There is consumer support for a public awareness campaign and regulatory approaches to reduce the amount of salt in the food supply. Multisector collaboration between the food industry, health agencies and government is required to improve public awareness and to reduce the salt content of foods to decrease population salt consumption in Australia.